I'm now 62, I have 2 sisters and we've been actively involved in Mom's care from the day she fell and broke her hip (2005). We did 24-hr homecare till we were all getting sick (I had 2 bouts with kidney stones while sleepign on her floor so I cd help her back into bed during the night.) I was workign full time also. My older sis and I have married kids and grandkids; my younger sis has no kids. She has no inkling of time, energy, emotion we put into our families (we both babysit quite frequently, which also requires travel time) as well as to Mom. I cannot handle her expectation around Mom, we're either arguing or not talking. She throws out "it's not about you," which pisses me off. My life has never been about me! We've become so close during all this but it's really fallen apart again. I have the best relationship with Mom I've ever had; she was very abusive of me growing up. I've done lots of therapy and moved on. But I'm so very tired of all this--so much for her, or our, quality of life...
Sorry you are exhausted. We all get that way at times.
DIAL IT DOWN. You are obviously spreading yourself too thin and biting off more than you can chew at this time.
DO NOT take on anymore responsibilities and cut back on what you have taken on currently. There HAS to be a few things that can get put aside until you are reguevinated. LIMITS!!!!!
RESPITE is the term for the day!!!!!
As far as your sisters...the worst and the best seem to come out at these times. In a perfect world, you would all work together equally. I haven't seen this yet.
However, please be careful about one thing...even though your younger sister does not have children, it does not make her any more responsible for your parents. Your decision to have a family (or not) has no bearing on your parent's care. (btw, could your married children pitch in to help?...it's their grandparents too.)
Good luck finding peace and a good medium.